tilepy: rapid tiling strategies in mid/small FoV observatories

The challenges inherent to time-domain multi-messenger astronomy require strategic actions so that adapted, optimized follow-up observations are performed efficiently. In particular, poorly localized events require dedicated tiling and/or targeted, follow-up campaigns so that the region in which the source really is can be efficiently covered, increasing the chances to detect the multi-wavelength counterpart. We have developed the python package "tilepy" to rapidly derive the observation scheduling of large uncertainty localization events by small/mid-FoV instruments. We will describe several mature follow-up scheduling strategies. These range from an option to use of low-resolution grids, to the full integration of sky regions and targeted observations using galaxy catalogs. The algorithms consider the visibility constraints of customisable observatories and allow to schedule observations in both astronomical darkness and in moonlight conditions. Developed initially to provide a rapid response to gravitational wave (GW) alerts by Imaging Atmospheric Cherenkov Telescopes (IACTs), they have been proven successful, as shown by the GW follow-up during O2 and O3 with the H.E.S.S. telescopes, and particularly in the follow-up of GW170817, the first binary neutron star (BNS) merger ever detected. Here we will present a generalisation of these rapid strategies to other alerts showing large uncertainties in the localization, like Gamma-Ray Burst (GRB) alerts from Fermi-GBM. We will also demonstrate the flexibility of {\it tilepy} in scheduling observations for a large variety of observatories. We will conclude by describing the latest developments of these algorithms that are able to derive optimised follow-up schedules across multiple observatories and networks of telescopes.Comment: Proceedings 38th International Cosmic Ray Conference (ICRC2023

Astro-COLIBRI: An Advanced Platform for Real-Time Multi-Messenger Astrophysics

Observations of transient phenomena like Gamma-Ray Bursts (GRBs), Fast Radio Bursts (FRBs), stellar flares and explosions (novae and supernovae), combined with the detection of novel cosmic messengers like high-energy neutrinos and gravitational waves has revolutionized astrophysics over the last years. The discovery potential of both ulti-messenger and multi-wavelength follow-up observations as well as serendipitous observations could be maximized with a novel tool which allows for quickly acquiring an overview over relevant information associated with each new detection. Here we present Astro-COLIBRI, a novel and comprehensive platform for this challenge. Astro-COLIBRI's architecture comprises a public RESTful API, real-time databases, a cloud-based alert system and a website as well as apps for iOS and Android as clients for users. Astro-COLIBRI evaluates incoming messages of astronomical observations from all available alert streams in real time, filters them by user specified criteria and puts them into their MWL and MM context. The clients provide a graphical representation with an easy to grasp summary of the relevant data to allow for the fast identification of interesting phenomena, provides an assessment of observing conditions at a large selection of observatories around the world, and much more. Here the key features of Astro-COLIBRI are presented. We outline the architecture, summarize the used data resources, and provide examples for applications and use cases. Focussing on the high-energy domain, we'll discuss the use of the platform in searches for high-energy gamma-ray counterparts to high-energy neutrinos, gamma-ray bursts and gravitational waves.Comment: Proceedings 38th International Cosmic Ray Conference (ICRC2023

Gammapy: A Python package for gamma-ray astronomy

In this article, we present Gammapy, an open-source Python package for the analysis of astronomical $\gamma$-ray data, and illustrate the functionalities of its first long-term-support release, version 1.0. Built on the modern Python scientific ecosystem, Gammapy provides a uniform platform for reducing and modeling data from different $\gamma$-ray instruments for many analysis scenarios. Gammapy complies with several well-established data conventions in high-energy astrophysics, providing serialized data products that are interoperable with other software packages. Starting from event lists and instrument response functions, Gammapy provides functionalities to reduce these data by binning them in energy and sky coordinates. Several techniques for background estimation are implemented in the package to handle the residual hadronic background affecting $\gamma$-ray instruments. After the data are binned, the flux and morphology of one or more $\gamma$-ray sources can be estimated using Poisson maximum likelihood fitting and assuming a variety of spectral, temporal, and spatial models. Estimation of flux points, likelihood profiles, and light curves is also supported. After describing the structure of the package, we show, using publicly available $\gamma$-ray data, the capabilities of Gammapy in multiple traditional and novel $\gamma$-ray analysis scenarios, such as spectral and spectro-morphological modeling and estimations of a spectral energy distribution and a light curve. Its flexibility and power are displayed in a final multi-instrument example, where datasets from different instruments, at different stages of data reduction, are simultaneously fitted with an astrophysical flux model.Comment: 26 pages, 16 figure

Observations de sursauts gamma avec des télescopes Cherenkov Gamma-Ray Bursts observations with Cherenkov telescopes : legs de H.E.S.S. et optimisation du suivi et de la détection avec le Large-Sized Telescopes de CTAes of CTA

Since the first detection of a Gamma-Ray burst by the Vela satellites in 1967, they have been studied across the whole light spectrum with detection at different wavelengths. They are also one of the first types of objects detected with multiple messengers by the codetection of gravitational waves and electromagnetic emission, with GW 170817.Cherenkov instruments have searched for a counterpart of GRBs at very high energies (above 100 GeV) for a long time. After more than two decades of effort, the H.E.S.S. telescopes achieved the first detection with GRB 180720B quickly followed by MAGIC with GRB190114C. Since these detections, GRBs emission started to be unveiled at VHE with the detection of two other GRBs.The next generation of Cherenkov telescopes (CTA) is currently being built. GRBs will be one of the key observation targets. LST-1, a prototype of large CTA telescope, is currently under commissioning at La Palma. Thanks to their performance, LST telescopes will be the main contributors of CTA to the detection of GRBs.A system called the bending model is in charge of the online correction of the pointing of telescopes, which is essential to correct systematic errors linked to the deformation of the lightweight structure. I have entirely developed the code, presented here, during my PhD. It takes care of the data acquisition, interacting with subsystem of the telescope, the data quality, the analysis and the determination of a deformation model. I have also worked on the integration of the program into the LST software framework.The observations of GRBs by LST-1 have already started. This was for the occasion to improve the follow-up strategy, especially when the alert comes from instruments with poor localization accuracy, like Fermi/GBM. On the analysis side, I have worked on the first background model for LST but also on the improvement of the sensitivity, either by searching for better selection criteria for the events or testing new reconstruction algorithms based on deep learning created at the LAPP.Finally, H.E.S.S. telescopes, in Namibia, have observed a lot of GRBs since 2004. A catalogue of all these observations and their results is under creation, intending to answer the question of why so many observations were performed without success before the detection of the first GRBs and why the ones detected have been and not the others. I was in charge of the analysis of all the data and the interpretation I made with my colleagues are presented here.Depuis les premières détections de sursaut gamma par les satellites Vela en 1967, ils ont été largement étudiés sur l'ensemble du spectre lumineux avec des détection à différentes longueurs d'onde. Ils ont été aussi un des premiers types d'objets détectés en astronomie multimessager avec la détection simultanée en ondes gravitationnelles et ondes lumineuse de GW 170817.Les télescopes Cherenkov ont cherché une contrepartie aux sursauts gamma à très haute énergie (au delà de 100 GeV) depuis longtemps. Après des années d'effort, les télescopes H.E.S.S. ont effectué la première détection avec GRB 180720B rapidement suivi par la détection de GRB 190114C par MAGIC. Depuis ces détections, l'émission de ces objets à très haute énergies a commencé à être dévoilé notamment avec l'aide de la détection de deux autres sursauts.La prochaine génération de télescopes Cherenkov, appelés CTA, est actuellement en cours de construction. Les sursauts gamma seront parmi les principales cibles d'observation. LST-1, qui est un télescope prototype pour CTA, est actuellement en phase de test à La Palma. Avec leur performance, les télescopes LST seront parmi les principaux contributeurs à la détection de sursauts pour CTA.Un système appelé bending model est en charge de la correction du pointé des télescopes durant les observations : il est en effet essentiel de corriger les erreurs systématiques de pointé du télescope, lié à la déformation de la structucture légère. J'ai entièrement développé le code, présenté ici, durant ma thèse. Il s'occupe de prendre les données, interagir avec les différents systèmes du télescope, de vérifier la qualité des données, de les analyser et de déterminer le modèle de déformation. J'ai également travaillé à l'intégration du programme au sein du système logiciel pour le contrôle du LST.Les observations de GRBs avec LST-1 ont déjà commencé. Cela est l'occasion d'améliorer les stratégies pour le suivi d'évènements, en particulier pour les alertes venant d'instruments avec des localisations peu précises comme Fermi/GBM. Du coté de l'analyse, j'ai travaillé sur les premiers modèles de fond du LST ainsi que à une amélioration de la sensibilité, soit en cherchant des meilleurs critères de sélections des évènements, ou en testant les nouveaux algorithmes de reconstruction utilisant le deep learning créé au LAPP.Finalement, H.E.S.S., installé en Namibie, à observé de nombreux sursauts depuis 2004. Un catalogue des observations et de leur résultats est en cours de création, avec comme objectif de répondre à la question de pourquoi autant de sursauts ont été observés sans succès avant les premières détections. J'étais en charge de l'analyse des données, et j'ai également travaillé à l'interprétation des données avec mes collègues dont les résultats sont présentés dans ce manuscrit

Observations de sursauts gamma avec des télescopes Cherenkov Gamma-Ray Bursts observations with Cherenkov telescopes : legs de H.E.S.S. et optimisation du suivi et de la détection avec le Large-Sized Telescopes de CTAes of CTA

Since the first detection of a Gamma-Ray burst by the Vela satellites in 1967, they have been studied across the whole light spectrum with detection at different wavelengths. They are also one of the first types of objects detected with multiple messengers by the codetection of gravitational waves and electromagnetic emission, with GW 170817.Cherenkov instruments have searched for a counterpart of GRBs at very high energies (above 100 GeV) for a long time. After more than two decades of effort, the H.E.S.S. telescopes achieved the first detection with GRB 180720B quickly followed by MAGIC with GRB190114C. Since these detections, GRBs emission started to be unveiled at VHE with the detection of two other GRBs.The next generation of Cherenkov telescopes (CTA) is currently being built. GRBs will be one of the key observation targets. LST-1, a prototype of large CTA telescope, is currently under commissioning at La Palma. Thanks to their performance, LST telescopes will be the main contributors of CTA to the detection of GRBs.A system called the bending model is in charge of the online correction of the pointing of telescopes, which is essential to correct systematic errors linked to the deformation of the lightweight structure. I have entirely developed the code, presented here, during my PhD. It takes care of the data acquisition, interacting with subsystem of the telescope, the data quality, the analysis and the determination of a deformation model. I have also worked on the integration of the program into the LST software framework.The observations of GRBs by LST-1 have already started. This was for the occasion to improve the follow-up strategy, especially when the alert comes from instruments with poor localization accuracy, like Fermi/GBM. On the analysis side, I have worked on the first background model for LST but also on the improvement of the sensitivity, either by searching for better selection criteria for the events or testing new reconstruction algorithms based on deep learning created at the LAPP.Finally, H.E.S.S. telescopes, in Namibia, have observed a lot of GRBs since 2004. A catalogue of all these observations and their results is under creation, intending to answer the question of why so many observations were performed without success before the detection of the first GRBs and why the ones detected have been and not the others. I was in charge of the analysis of all the data and the interpretation I made with my colleagues are presented here.Depuis les premières détections de sursaut gamma par les satellites Vela en 1967, ils ont été largement étudiés sur l'ensemble du spectre lumineux avec des détection à différentes longueurs d'onde. Ils ont été aussi un des premiers types d'objets détectés en astronomie multimessager avec la détection simultanée en ondes gravitationnelles et ondes lumineuse de GW 170817.Les télescopes Cherenkov ont cherché une contrepartie aux sursauts gamma à très haute énergie (au delà de 100 GeV) depuis longtemps. Après des années d'effort, les télescopes H.E.S.S. ont effectué la première détection avec GRB 180720B rapidement suivi par la détection de GRB 190114C par MAGIC. Depuis ces détections, l'émission de ces objets à très haute énergies a commencé à être dévoilé notamment avec l'aide de la détection de deux autres sursauts.La prochaine génération de télescopes Cherenkov, appelés CTA, est actuellement en cours de construction. Les sursauts gamma seront parmi les principales cibles d'observation. LST-1, qui est un télescope prototype pour CTA, est actuellement en phase de test à La Palma. Avec leur performance, les télescopes LST seront parmi les principaux contributeurs à la détection de sursauts pour CTA.Un système appelé bending model est en charge de la correction du pointé des télescopes durant les observations : il est en effet essentiel de corriger les erreurs systématiques de pointé du télescope, lié à la déformation de la structucture légère. J'ai entièrement développé le code, présenté ici, durant ma thèse. Il s'occupe de prendre les données, interagir avec les différents systèmes du télescope, de vérifier la qualité des données, de les analyser et de déterminer le modèle de déformation. J'ai également travaillé à l'intégration du programme au sein du système logiciel pour le contrôle du LST.Les observations de GRBs avec LST-1 ont déjà commencé. Cela est l'occasion d'améliorer les stratégies pour le suivi d'évènements, en particulier pour les alertes venant d'instruments avec des localisations peu précises comme Fermi/GBM. Du coté de l'analyse, j'ai travaillé sur les premiers modèles de fond du LST ainsi que à une amélioration de la sensibilité, soit en cherchant des meilleurs critères de sélections des évènements, ou en testant les nouveaux algorithmes de reconstruction utilisant le deep learning créé au LAPP.Finalement, H.E.S.S., installé en Namibie, à observé de nombreux sursauts depuis 2004. Un catalogue des observations et de leur résultats est en cours de création, avec comme objectif de répondre à la question de pourquoi autant de sursauts ont été observés sans succès avant les premières détections. J'étais en charge de l'analyse des données, et j'ai également travaillé à l'interprétation des données avec mes collègues dont les résultats sont présentés dans ce manuscrit

Astro-COLIBRI: An Advanced Platform for Real-Time Multi-Messenger Astrophysics

Observations of transient phenomena like Gamma-Ray Bursts (GRBs), Fast Radio Bursts (FRBs), stellar flares and explosions (novae and supernovae), combined with the detection of novel cosmic messengers like high-energy neutrinos and gravitational waves has revolutionized astrophysics over the last years. The discovery potential of both ulti-messenger and multi-wavelength follow-up observations as well as serendipitous observations could be maximized with a novel tool which allows for quickly acquiring an overview over relevant information associated with each new detection. Here we present Astro-COLIBRI, a novel and comprehensive platform for this challenge. Astro-COLIBRI's architecture comprises a public RESTful API, real-time databases, a cloud-based alert system and a website as well as apps for iOS and Android as clients for users. Astro-COLIBRI evaluates incoming messages of astronomical observations from all available alert streams in real time, filters them by user specified criteria and puts them into their MWL and MM context. The clients provide a graphical representation with an easy to grasp summary of the relevant data to allow for the fast identification of interesting phenomena, provides an assessment of observing conditions at a large selection of observatories around the world, and much more. Here the key features of Astro-COLIBRI are presented. We outline the architecture, summarize the used data resources, and provide examples for applications and use cases. Focussing on the high-energy domain, we'll discuss the use of the platform in searches for high-energy gamma-ray counterparts to high-energy neutrinos, gamma-ray bursts and gravitational waves

Detection of new Extreme BL Lac objects with H.E.S.S. and Swift XRT

International audienceExtreme high synchrotron peaked blazars (EHBLs) are amongst the most powerful accelerators found in nature. Usually the synchrotron peak frequency of an EHBL is above $10^{17}$ Hz, i.e., lies in the range of medium to hard X-rays making them ideal sources to study particle acceleration and radiative processes. EHBL objects are commonly observed at energies beyond several TeV, making them powerful probes of gamma-ray absorption in the intergalactic medium. During the last decade, several attempts have been made to increase the number of EHBL detected at TeV energies and probe their spectral characteristics. Here we report new detections of EHBLs in the TeV energy regime, each at a redshift of less than 0.25, by the High Energy Stereoscopic System (H.E.S.S.). Also, we report on X-ray observations of these EHBLs candidates with Swift-XRT. In conjunction with the very high energy observations, this allows us to probe the radiation mechanisms and the underlying particle acceleration processes

Follow-up of gravitational waves alerts with IACTs using Astro-COLIBRI

International audienceFollow-up of gravitational wave alerts has proven to be challenging in the past due to the large uncertainty on the localisation, much larger than the field of view of most instruments. A smart pointing strategy helps to increase the chance of observing the true position of the underlying compact binary merger event and so to detect an electromagnetic counterpart. To tackle this, a software called tilepy has been developed and was successfully used by the H.E.S.S. collaboration to search for very-high energy gamma-ray emission from GWs during the O2 and O3 runs. The optimised tiling strategies implemented in tilepy allowed H.E.S.S. to be the first ground facility to point toward the true position of GW 170817. Here we present the main strategy used by the software to compute an optimal observation schedule. The Astro-COLIBRI platform helps to plan follow-up of a large range of transient phenomena including GW alerts. The integration of tilepy in this tool allow for an easy planning and visualisation of of follow-up of gravitational wave alert helping the astronomer to maximise the chance of detecting a counterpart. The platform also provides an overview of the multi-wavelength context by grouping and visualising information coming from different observatories alongside GW alerts

Follow-up of gravitational waves alerts with IACTs using Astro-COLIBRI

International audienceFollow-up of gravitational wave alerts has proven to be challenging in the past due to the large uncertainty on the localisation, much larger than the field of view of most instruments. A smart pointing strategy helps to increase the chance of observing the true position of the underlying compact binary merger event and so to detect an electromagnetic counterpart. To tackle this, a software called tilepy has been developed and was successfully used by the H.E.S.S. collaboration to search for very-high energy gamma-ray emission from GWs during the O2 and O3 runs. The optimised tiling strategies implemented in tilepy allowed H.E.S.S. to be the first ground facility to point toward the true position of GW 170817. Here we present the main strategy used by the software to compute an optimal observation schedule. The Astro-COLIBRI platform helps to plan follow-up of a large range of transient phenomena including GW alerts. The integration of tilepy in this tool allow for an easy planning and visualisation of of follow-up of gravitational wave alert helping the astronomer to maximise the chance of detecting a counterpart. The platform also provides an overview of the multi-wavelength context by grouping and visualising information coming from different observatories alongside GW alerts

Follow-up of gravitational waves alerts with IACTs using Astro-COLIBRI

International audienceFollow-up of gravitational wave alerts has proven to be challenging in the past due to the large uncertainty on the localisation, much larger than the field of view of most instruments. A smart pointing strategy helps to increase the chance of observing the true position of the underlying compact binary merger event and so to detect an electromagnetic counterpart. To tackle this, a software called tilepy has been developed and was successfully used by the H.E.S.S. collaboration to search for very-high energy gamma-ray emission from GWs during the O2 and O3 runs. The optimised tiling strategies implemented in tilepy allowed H.E.S.S. to be the first ground facility to point toward the true position of GW 170817. Here we present the main strategy used by the software to compute an optimal observation schedule. The Astro-COLIBRI platform helps to plan follow-up of a large range of transient phenomena including GW alerts. The integration of tilepy in this tool allow for an easy planning and visualisation of of follow-up of gravitational wave alert helping the astronomer to maximise the chance of detecting a counterpart. The platform also provides an overview of the multi-wavelength context by grouping and visualising information coming from different observatories alongside GW alerts